Cecropia cocoons bewilder a beginner by their difference in shape.  You cannot determine the sex of the moth by the size of the cocoon.  In the case of the twins, the cocoon of the female was the larger; but I have known male and female alike to emerge from large or small.  You are fairly sure of selecting a pair if you depend upon weight.  The females are heavier than the males, because they emerge with quantities of eggs ready to deposit as soon as they have mated.  If any one wants to winter a pair of moths, they are reasonably sure of doing so by selecting the heaviest and lightest cocoons they can find.

In the selection of cocoons, hold them to the ear, and with a quick motion reverse them end for end.  If there is a dull, solid thump, the moth is alive, and will emerge all right.  If this thump is lacking, and there is a rattle like a small seed shaking in a dry pod, it means that the caterpillar has gone into the cocoon with one of the tiny parasites that infest these worms, clinging to it, and the pupa has been eaten by the parasite.

In fall and late summer are the best times to find cocoons, as birds tear open many of them in winter; and when weatherbeaten they fade, and do not show the exquisite shadings of silk of those newly spun.  When fresh, the colours range from almost white through lightest tans and browns to a genuine red, and there is a silvery effect that is lovely on some of the large, baggy ones, hidden under bridges.  Out of doors the moths emerge in middle May or June, but they are earlier in the heat of a house.  They are the largest of any species, and exquisitely coloured, the shades being strongest on the upper side of the wings.  They differ greatly in size, most males having an average wing sweep of five inches, and a female that emerged in my conservatory from a cocoon that I wintered with particular care had a spread of seven inches, the widest of which I have heard; six and three quarters is a large female.  The moth, on appearing, seems all head and abdomen, the wings hanging limp and wet from the shoulders.  It at once creeps around until a place where it can hang with the wings down is found, and soon there begins a sort of pumping motion of the body.  I imagine this is to start circulation, to exercise parts, and force blood into the wings.  They begin to expand, to dry, to take on colour with amazing rapidity, and as soon as they are full size and crisp, the moth commences raising and lowering them slowly, as in flight.  If a male, he emerges near ten in the forenoon, and flies at dusk in search of a mate.